The invention relates to an internal combustion engine, particularly an internal combustion engine with an exhaust gas re-circulation system including an exhaust gas re-circulation line, which branches off an exhaust gas pipe and returns exhaust gas to an engine intake duct and which includes a valve for controlling the re-circulation flow of the exhaust gas.
Such an internal combustion engine is described for example in DE 195 24 603 C1. The known internal combustion engine includes an exhaust gas re-circulation system by way of an exhaust gas re-circulation line, which branches off an exhaust pipe and re-circulates exhaust gases to a charge air intake duct. The exhaust gas re-circulation line includes a shutoff valve which, depending on its position, permits, or blocks, passage of exhaust gases through the re-circulation line. During normal operation with exhaust gas re-circulation, the shut-off valve is closed when the engine power output is above a certain value since otherwise the charge air pressure in the intake duct would be higher than the exhaust gas pressure in the exhaust gas line so that no exhaust gas could flow through the exhaust gas re-circulation line.
The shutoff valve is a plate valve whose valve plate is biased by a valve spring onto an annular valve seat disposed in the exhaust gas re-circulation line. In an embodiment provided for commercial vehicles the shutoff valve opens against the flow direction of the exhaust gas to be re-circulated in order to prevent opening of the valve by the high exhaust gas pressure forces occurring in the exhaust gas duct during engine braking operation. These forces might otherwise exceed the closing forces of the valve spring whereby the valve would be pushed open resulting in a loss of engine braking power.
The shutoff valve is arranged at the point where the exhaust gas re-circulation line branches off the exhaust gas line and includes a tubular valve housing which forms a beginning section of the exhaust gas re-circulation line. The exhaust gas re-circulation line extends then from the valve housing at a right angle so that a valve spring and a valve operating membrane can be arranged in alignment with the tubular housing.
The shutoff valve opens into the exhaust gas line in such a way that the exhaust gas flow can pass the valve plate extending normal to the exhaust gas flow.
The known internal combustion engine has the disadvantage that, when the shutoff valve is open, the valve plate acts as a baffle plate generating a high flow resistance. The deflection of the exhaust gases necessitated by the design of the shutoff valve also results in an increased flow resistance. In order to provide for a flow of exhaust gas from the exhaust pipe to the intake duct, the exhaust gas pressure in the exhaust pipe must be higher than the intake air pressure in the intake duct. The pressure level required to be present in the exhaust pipe for the re-circulation of the exhaust gas depends among others on the flow resistance in the exhaust gas re-circulation line. In order to overcome the relatively high flow resistance caused by the shutoff valve, the pressure in the exhaust pipe must be relatively high to overcome the gas flow resistance which detrimentally affects fuel consumption of the engine.
Furthermore, the shutoff valve of the prior art arrangement is not provided with a firm stop at its open end position and can therefore be subject to oscillations because of pressure pulsations in the exhaust gas flow. As a result the free flow cross-section is reduced and the re-circulated exhaust gas volume becomes too small that is it deviates from the desired value.
In order to facilitate the flow of exhaust gases around the valve plate when the shutoff valve is open, in the arrangement shown in the patent publication the shutoff valve must be arranged exactly at the branch-off location of the exhaust gas re-circulation line and must open into this line. Otherwise, the exhaust gas re-circulation line needs to include a section of increased diameter in which the valve plate is accommodated in the open position of the shutoff valve. However, it is a disadvantage that, in the first case, the position of the exhaust valve is predetermined and cannot be changed, and, in the second case, the manufacturing costs are higher and the arrangement is larger and requires an increased amount of space.
It is the object of the present invention to provide an internal combustion engine with an exhaust gas re-circulation system of the type referred to above which, however, has low flow losses in the exhaust gas re-circulation pipe and wherein the position of the valve in the exhaust gas re-circulation line can be selected freely and in a space-saving manner.